This invention relates generally to apparatus for cutting threaded rods to any required lengths without ruining the threads thereon, and more specifically to a machine comprising a fixed and a movable cutting bit, the latter being power driven for linear travel relative to the fixed cutting bit for cutting threaded rods. Still more specifically, the invention deals with provisions in such shearing machines for protecting the semicircular internal screw threads which are formed at least on the fixed cutting bit, from being damaged or broken when the rod is cut.
Portable, power-driven cutting machines have been known which cut threaded rods by linear travel of a movable cutting bit relative to a fixed cutting bit. An example of such cutting machine has a bladelike a punch as a movable cutting bit, and a die as a fixed cutting bit. A threaded rod is cut by punching, that is, by thrusting the punch into the cavity in the die, with the consequent removable of part of the threaded rod. Another example of cutting machine cuts threaded rods by the shearing action of the fixed and movable cutting bits.
In the punching machine, only the die has a series of semicircular internal screw threads of the same pitch as that of the thread on the rod to be cut, for mating engagement therewith. Both cutting bits of the shearing machine, on the other hand, have similar internal threads for mating engagement with the thread on the rod.
The cutting machines of both types offer the advantage that threaded rods can be readily cut to any required lengths without ruining the threads thereon, with the result that mating nuts can be smoothly turned onto such rod lengths. There has been a problem, however, that has been left unsolved with such cutting machines.
Take the punching machine for example. The internal threads on the die have so far been of the same shape and size as the thread on the rods to be cut, so that contact between them have been made only as at their flanks. Consequently, the die has had to bear the impact of cutting at the flanks of its internal threads. The force thus exerted on the die includes a component normal to the flanks, so that the threads, particularly those lying next to the die cavity, have been susceptible to fracture or breakage. As these particular threads are broken, so are the cutting edges of the die. The die with the fractured or broken threads have therefore had to be replaced.